An image recognition device recently increases in need for recognizing, e.g., in a lane keep system, a road position from an image taken by an in-vehicle camera. The image recognition device imports an image from an in-vehicle camera into a memory and processes the imported image with respect to the respective pixels, thereby detecting (or recognizing) a road position. However, processing with respect to the respective pixels needs a long period for detecting the road position, so that a high-speed detection for the road position is hardly achieved.
A dynamic contour extraction method of extracting a contour of a specific recognition object included in an image is therefore proposed in use for detecting the road position. The dynamic contour extraction method includes known SNAKE, where a curve with control points is disposed in an image; an internal energy Eint indicating smoothness of the curve, an image energy Eimage, and an external energy Eext are summed up; the curve is modified so that the summed total energy becomes the minimum; and the contour of the recognition object included in the image is thereby detected (refer to JP-2002-049922 A).
An application of SNAKE to road recognition is shown in FIG. 6. Here, a dynamic contour model is formed of two curves (straight lines in FIG. 6) with control points shown as closed circles (●) in FIG. 6. The control points are moved and converged for detecting the road position in such a manner that the respective curves of the contour model approach from the inside to left and right road boundaries to thereby minimize the total energy (refer to “Active contour road model for road tracking and 3D road shape reconstruction” by Yasushi YAGI and other three persons, Transaction of the Institute of Electronics, Information and Communication Engineers, p. 1597-1607, Vol. J84-D-II No. 8, August 2001).
However, the above method cannot detect a road position from an image of the scene where crossroads or a left or right turn lane exists ahead of the camera, as described by the authors. Additionally, SNAKE can generally extract a contour of a recognition object in an image only using a closed curve (or closed curved surface).